1. Field of the Invention
The present invention relates in general to a vitrified bond tool, and more particularly to such a vitrified bond tool including super abrasive grains and used as a dressing tool for dressing a polishing tool such as a polishing pad which is used for a chemical mechanical polishing of a semiconductor wafer.
2. Discussion of the Related Art
In a process of manufacturing a semiconductor, there is commonly practiced a chemical mechanical polishing (herein after referred to as “CMP”) operation. In recent years, since a larger number of sheets of wafers are laminated with a larger scale of integration of electronic circuit, CMP operation is widely practiced for flattening surfaces of the wafers. In CMP operation, a polishing pad and a semiconductor wafer are rotated relative to each other, with application of a polishing fluid including fine abrasive grains to the polishing pad, for polishing the semiconductor wafer. In CMP operation for a semiconductor wafer, a high degree of flatness in the polished surface of the wafer is required by polishing a considerably small amount of the surface of the wafer. For satisfying this requirement, the polishing pad has to be dressed very frequently. The polishing pad has been conventionally dressed by using an electro-deposited diamond tool, which includes a base metal made of stainless or other metallic material, and diamond abrasive grains bonded to the base metal with Ni metal (electro-deposition bond).
JP-A-10-71559 discloses a dresser for dressing a polishing pad used for polishing a semiconductor wafer. This dresser includes a base metal and a diamond thin film. The base metal has, in its working surface, a multiplicity of protrusions formed by using a wire-EDM (electro-discharge machining) or a metallic mold. The diamond thin film is formed on the working surface of the base metal by a vapor phase synthetic method.
JP-A-10-193266 discloses a method of a vitrified bond tool, which was proposed by the present inventors. This method is characterized by including the step of positioning a screen having a predetermined printing pattern, on a support body; the step of applying a paste including abrasive grains and vitrified bond which are dispersed in the paste, onto the support body through the screen; and the step of sintering the applied paste.
However, the operation for dressing the polishing pad with the electro-deposited diamond tool, in which the diamond abrasive grains are bonded to the base metal by Ni metal as an electro-deposition bond, suffers from elution of Ni metal into the polishing fluid whereby the workpiece is contaminated by Ni metal, particularly, where the polishing fluid is a strong-acid fluid. Further, the electro-deposited diamond tool has a drawback that all of the abrasive grains are not bonded to the base metal with sufficiently large bonding strength, due to the random arrangement of the abrasive grains in the abrasive layer, so that some of the abrasive grains which are not firmly bonded to the base metal are removed from the base metal and accordingly stay on the polishing pad. The workpiece is scratched or damaged by the abrasive grains thus staying on the polishing pad.
The dresser disclosed in JP-A-10-71559, in which abrasive grains are not used, requires a process of forming the multiplicity of protrusions in its base metal and also a process of forming the diamond thin film by the vapor phase synthetic method, thereby resulting in a considerably increased manufacturing cost. Dressers disclosed in JP-A-10-44023 and JP-A-10-138120 are costly to manufacture, too.
In the method disclosed in JP-A-10-193266, in which the paste including the abrasive grains and the vitrified bond therein is applied onto the support body through the screen, the abrasive grains are unlikely to be sufficiently dispersed in the paste, due to possible sedimentation of the abrasive grains, where each of the abrasive grains has a diameter larger than 40 μm. Thus, the paste applied onto the support body could be fixed to the support body in the sintering step, with agglomeration of the abrasive grains.